1. Field of the Invention
This invention relates to a layout structure for electrophotographic photocopiers, printers, recording apparatuses, and the like.
2. Description of Related Art
Multicolor image forming apparatuses using an electrophotographic method tend to require an increased number of developing units and complicated processes, such as development and transfer in overlapping the respective colors, and fixture of multi-layer toners, in comparison with conventional monochrome engines. Those apparatuses are further subject, with high frequency, to replacement of electrostatic latent image forming bodies, such as color developers and photosensitive bodies, and a jamming recovery operation for the engine is also needed. Therefore, an engine structure excellent in maintenance and jamming recovery property is demanded.
FIG. 6 shows a perspective view of a conventional example. A primary charger, a developing unit, and a transfer charger (all not shown) are disposed around each photosensitive drum, and form respective units as process cartridges 1a to 1d. Numeral 5 denotes a fixing unit; numeral 4 denotes a feeding cassette; numeral 3 denotes a secondary transfer roller; numeral 2 denotes an intermediate transfer belt (intermediate transfer body); and numeral 7 denotes a delivery tray.
During maintenance of the process cartridges 1a to 1d, a side door 10 is opened to allow the process cartridges 1a to 1d to be pulled out. As shown in FIG. 7, the intermediate transfer belt 2 is then moved in a direction of arrow X to release pressure between the intermediate transfer belt 2 and the photosensitive drums 20a to 20d of the process cartridges 1a to 1d. 
The process cartridges 1a to 1d are made to slide in a direction of arrow Y as shown in FIG. 6, and new process cartridges 1a to 1d are inserted. When a transfer material is jammed in a conveyance route 25, a front door 11 is openable in a front and back direction at the conveyance route 25 to allow jamming treatment.
In Japanese Patent Application Publication JP-A-11-133,694, to improve jamming recovery and controllability, a mechanism in which the transfer portion is openable forwardly around an apparatus lower portion as a center, and a mechanism in which the photosensitive body belt portion is lifted upward around an apparatus rear portion as a center are provided, thereby allowing maintenance work and paper jamming recovery.
With the multicolor image forming apparatus as shown in FIGS. 6 and 7, however, the accessing directions for replacement of the process cartridges and paper jamming recovery are on the apparatus front and side, so that there is a problem that a larger working space is necessary. It is disadvantageous that the apparatus side space is required during pulling out and inserting of the process cartridges. Furthermore, the apparatus tends to be larger and more complicated due to a moving mechanism of the intermediate transfer belt for releasing pressure between the intermediate transfer belt and the photosensitive drum of the process cartridge during replacement of the process cartridge, thereby increasing the cost of the apparatus.
Because a sliding mechanism for pulling out and inserting the process cartridges is inevitably provided, the apparatus tends to be larger and more complicated. In the publication JP-A-11-133,694, when the operator conducts the maintenance work for the photosensitive bodies or the like while standing at a front side, the apparatus is structured as not to open the photosensitive belt unit upward unless the transfer unit is made open toward the front side about a pivot at the apparatus lower portion, and therefore, there arises problems such that not only the transfer portion opened toward the front side may become disturbed, but also the operator cannot easily access the developing unit or the like when two opening operations are needed. Moreover, other conventional designs relating to the opening and closing operation of the apparatuses are exemplified in Japanese Patent Application Publications JP-A-10-307,439 and JP-A-2002-6583.